What is the scientific basic for the ancient romas choice of grape juice and grain product for growing yeast?

The ancient Romans utilized Grape Juice and grain products for yeast cultivation due to their natural sugar content, which provides a suitable environment for fermentation. The sugars in grape juice, primarily glucose and fructose, can be readily converted to alcohol and carbon dioxide by yeast. Similarly, grains contain starches that can be broken down into fermentable sugars through enzymatic activity, particularly when malted. This dual sourcing allowed for diverse fermentation processes, crucial for producing wine and bread.